Tomographic imaging is a signal acquisition and processing technology that allows for high-resolution cross-sectional imaging in biological systems. Tomographic imaging systems include, for example, optical coherence tomography systems, ultrasound imaging systems, and computed tomography. Tomographic imaging is particularly well-suited for imaging the subsurface of a vessel or lumen within the body, such as a blood vessel, using probes disposed within a catheter through a minimally invasive procedure.
Typical tomographic imaging catheters consist of an imaging core that rotates and moves longitudinally through a blood vessel, while recording an image video loop of the vessel. The motion results in a 3D dataset, where each frame provides a 360 degree slice of the vessel at different longitudinal section. These frames provide cardiologists with invaluable information such as the location and severity of the stenosis in a patient, the presence of vulnerable plaques, and changes in cardiovascular disease over time. The information also assists in determining the appropriate treatment plan for the patient, such as drug therapy, stent placement, angioplasty, bypass surgery, valve replacement, etc.
Generally, to graphically analyze tomographic images, a clinician scrolls through a series of image frames and manually performs various measurements on the anatomical structure of interest. In some instances, a computational algorithm is also used to calculate various anatomical measurements and display their numerical values to an image display screen. While the numerical output provides useful information, it is time consuming to evaluate and compare a large data set of tomographic images by scrolling through frames of images. The extended periods of scrutiny also lead to mental fatigue, and in turn, may lead to observer error.
In addition to evaluating vasculature, tomographic imagining may also be used to place or evaluate vascular stents. A stent is a small, tube-like structure made of a metal or polymer that is inserted into a blood vessel to hold the vessel open and keep it from occluding blood flow. A stent can also be used to reinforce an area of a vessel where the wall tissues are thin or calcification has formed. Typically, a stent is placed with a balloon catheter after the vessel has been imaged.
There are several risks associated with stent placement, however. For example, the stent can cause vascular lesions that may later embolize (dislodge and block vasculature). To avoid lesions, the stent should be placed in parallel within the vessel and the stent should uniformly contact the vessel wall during deployment. Additionally, it is critical that there is no dead space between the stent and the vessel wall because of a risk of a subsequent blockage or thrombus because of blood pooling or clotting between the stent and the vessel wall. (A stent that has been placed with gaps between the stent and the vessel wall is said to be in “incomplete apposition.”) Therefore, it is critical to verify that the stent is properly placed.
When tomographic imaging is used to evaluate a stent (or other medical device) many of the same issues arise with respect to overwhelming sets of images and fatigue related to processing the images. In addition, it can be difficult to immediately discern problematic placement of a medical device because of the visual similarity between a properly and improperly placed device when the images are displayed on a computer monitor, for example.